On 08/08/2017 06:06 PM, Alan Stern wrote:
> On Tue, 8 Aug 2017, Hannes Reinecke wrote:
>> On 08/08/2017 05:25 PM, Alan Stern wrote:
>>> On Tue, 8 Aug 2017, Hannes Reinecke wrote:
>>>> When checking the model and vendor string we need to use the
>>>> minimum value of either string, otherwise we'll miss out on
>>>> wildcard matches.
>>>> And we should avoid matching anything with zero size as this
>>>> match will be incorrect.
>>>> Without this patch certain Hitachi arrays will not be presenting
>>>> VPD pages correctly.
>>>> Fixes: 5e7ff2c ("SCSI: fix new bug in scsi_dev_info_list string matching")
>>>> Signed-off-by: Hannes Reinecke <h...@suse.com>
>>> This is very questionable.  As described in commit b704f70ce200 ("SCSI: 
>>> fix bug in scsi_dev_info_list matching"), there are devices which have 
>>> vendor or model strings of length 0, and there are entries in the 
>>> global device list like that too.  With this patch, such devices and 
>>> such entries would never match anything.
>>> Also, the idea of using the minimum length of either string doesn't 
>>> sound right.  It would allow a device with string "abc" to match an 
>>> entry in the list with string "abcd", which would be wrong.
>>> Suggestion:
>>>     Allow a device string to match a list entry if the lengths
>>>     are equal or the list entry is shorter (this would be a 
>>>     wildcard match), but not if the list entry is longer.  Here
>>>     the device string length is after leading and trailing blanks
>>>     have been removed.
>>>     As a corollary, allow an empty device string to match an empty 
>>>     list entry but nothing else.
>>> Alan Stern
>> Well, so far we haven't encountered any of those devices.
> But what if we do in the future?  The code should be correct for 
> anything.
>> I _have_ validated the patch with the known problematic inquiry strings,
>> namely
>> "Inateck" "       "
>> "       " "Scanner"
>> "Promise" "STEX"
>> and it gives the correct result for all of these.
> How can "       " "Scanner" give the correct result?  Oh, I see -- the 
> patch description and the code comment both say that empty strings 
> never match, but in fact they do -- you allow a match if either the 
> vendor or model string is empty, but not if they are both empty.
Yeah, should've clarified that.

>> If you have any inquiry strings for which this does _not_ produce the
>> correct result please let me know.
> What about "HITA" "OPEN-V"?  Or "" "OPEN-V"?  Both of these will match
> the "HITACHI" "OPEN-" entry, but neither of them should.
Hmm. "HITA" should not match the "HITACHI"; the search string is always
the full string, and only the devinfo string should be treated as partial.
Some goes for "".

> What about "ABCD" "Scanner"?  This will match the "        " "Scanner" 
> entry, but it shouldn't.
Hmm. Might be. But now we can test this with the scsi_debug module.
I'll be checking and report the results.


Dr. Hannes Reinecke                Teamlead Storage & Networking
h...@suse.de                                   +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)

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